<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    var tizhong = parseFloat(prompt('请输入你的体重：kg', '55'));
    var hegiht = parseFloat(prompt('请输入您的身高：li', '172'));

    let bz = tizhong - (hegiht - 108) * 2;
    if (bz > 10) {
      alert("偏胖");
    } else if (bz < -10) {
      alert('偏瘦');
    } else {
      alert('正常范围');
    }
  </script>
</body>

</html>